Spenser takes up a seemingly open and closed cold case at the behest of a street-wise teen-age girl, who believes her mother's murderers went free. As Spenser digs deeper into the mystery, he finds a much more dangerous and complex mystery than he bargained for. When fourteen-year-old Mattie Sullivan asks Spenser to look into her mother's murder, he's not completely convinced by her claim that the police investigation four years ago was botched. Mattie is gruff, street-smart, and wise beyond her years, left to care for her younger siblings and an alcoholic grandmother in a dilapidated apartment in South Boston. But her need for closure and her determination to make things right hit Spenser where he lives, they're the very characteristics he abides by.